1. Field of the Invention
The present general inventive concept relates to an image processing apparatus and a method thereof, and more specifically, to an image processing apparatus using a judder-map to prevent judder on CGI (Computer Graphic Imagery) or subtitles where pulldown technologies are not applied, and a method thereof.
2. Description of the Related Art
Image display devices usually operate in interlace scan or progressive scan mode. Interlace scanning, which is used in traditional TV systems, refers to a method of dividing each image frame into two fields and reading out lines in an odd/even sequence. The two fields are called the top/bottom fields, upper/lower fields, or odd/even fields. In contrast, progressive scanning (or non-interlace scan), which is generally used in computer monitors and digital TVs, refers to a method for representing moving images on a display screen, in which every pixel is represented in each frame and a full frame is drawn at one time.
For example, in 480-line NTSC (National Television System Committee) interlace scanning, a single frame is composed of two fields, each of 240 lines, presented every 1/60 of a second, which are interlaced to form a full picture (i.e., a 480-line image) every 1/30 second. Progressive scanning, on the other hand, draws a full picture (i.e., a 480-line image) every 1/60 second. Therefore, progressive scan images produce sharper, crisper edges of moving objects, whereas interlace scan images appear blurred on the edges of moving objects.
One of the most common examples of the use of the progressive scanning is motion picture film. Most movies released on DVD in recent years were originally captured on film. Unlike NTSC TVs, film is shown at 24 frames a second. Of course, it is possible to capture or store 24 original film frames directly on a DVD. However, the majority of image display devices, TVs for example, on the market create a picture using interlace scanning. Because of this trend, higher demands are being placed on the interlace scan DVDs, not the progressive scan DVDs.
Therefore, a 24-frame film in the progressive format needs to be converted to 60 fields in the interlace format. This is called 3:2 pulldown or telecine conversion. With the 3:2 pulldown method, two film frames at 24 Hz are converted to five fields at 60 Hz. In a case of transferring motion picture film to a video format, such as TV, based on PAL or SECAM system, 25 frames per second are converted into 50 fields, i.e., 2 fields per frame. This method of scanning 2 fields onto a frame is commonly referred to as 2:2 pulldown.
FIG. 1 is a diagram explaining 3:2 pulldown. Referring to FIG. 1, 24-frame progressive-scanned images per second are converted to interlaced images at 60 Hz. In other words, as can be seen in FIG. 1, 3 fields are produced from Frame 1, and two fields are produced from Frame 2. Overall, 5 fields are produced from every two frames.
Recently, there has been a gradual increase of image display devices using progressive scanning, and thus, it has become necessary to exchange data between display devices using different scan systems. In other words, there was a need to develop an IPC (Interlaced-to-Progressive Conversion) method converting an interlaced image to a progressive image. In the IPC process, if a field to be interpolated is a 3:2 pulldown format image, interlaced fields are combined to get a full progressive format image before they are 3:2 pulled down. Therefore, prior to the IPC, it is necessary to find out whether or not a field to be interpolated is a 3:2 pulldown image. Fortunately, there are many techniques for detecting 3:2 pulldown format images.
The following will now explain how to detect a 3:2 pulldown image.
Suppose that there are 10 fields, F1, F2, F3, F4, F5, F6, F7, F8, F9, and F10, which are 3:2 pulled down. Then, detection of a 3:2 pulldown image is accomplished by using the fact that the period of SAD (Sum of Absolute Difference) is 5. Given that two fields are separated by a period, the SAD of F1-F3, F6-F8 becomes extremely small (if there is no noise, the SAD is approximately zero). The SAD becomes very small because an original field is subtracted from a repeat field. Based on its regularity, the detection of a 3:2 pulldown image is accomplished by taking, per pixel, an absolute value of the subtraction between two fields that are always separated by 1/30 second, and summing the absolute value results for all the pixels to produce interim data. For instance, suppose that |F1-F3|=D1, |F2-F4|=D2, |F3-F4|=D3, . . . . Then, SAD, D1, and D6 have very small values, whereas the others have very large values. Moreover, the respective SADs are small, large, large, large, and large, showing some regularity.
However, when scenes are cut out the regularity of the SADs may disappear. In that case, judder results during the reverse 3:2 pulldown. Also, judder arises in CGI (Computer Graphic Imagery) or subtitles where 3:2 pulldown technologies are not applied.